Inkjet printing is a non-impact method for producing images by the deposition of liquid ink drops in response to digital signals. In a typical application, the viewable image is obtained by applying liquid ink in a pixel-by-pixel manner to the ink-receiving layer (IRL) of a recording element. There are numerous schemes which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to the ink sump. In another process, known as drop-on-demand (DOD) ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation.
Most inks commonly used in DOD inkjet printers are water-based. As such, for most outdoor applications and many indoor applications, images generated by inkjet printing with water-based inks must be laminated or otherwise protected from the elements. This requires the application of an additional layer over the image after it is printed.
The solution to the problem has been approached in many ways. For example, unexamined Japanese Patent Application #8 [1996]-282090 discloses a recording medium and image formation method in which the recording medium comprises a heat-fusible layer on a substrate, and which further comprises an ink-receiving layer containing both a pigment and a binder laminated on top of the heat-fusible layer. The recording medium is imaged with small droplets of ink and then heated. This application describes a multi-layer inkjet receiver, in which heat fusible particles are located in a layer below the topmost layer. With such a geometry, the particles' ability to interact with the ink colorant is severely reduced from the case where heat-fusible particles are at the free surface as described here.
U.S. Pat. No. 5,374,475 discloses a recording element useful for both xerographic and inkjet printing which comprises a "micro-porous layer consisting of a thermoplastic polymer free of filler material . . . such that the micro-porous structure can be eliminated by the application of heat and pressure." In one embodiment the micro-porous layer is prepared by coating a dispersion or suspension of thermoplastic particles without added binder. One problem with this approach is that the thermoplastic particle is prone to dusting and/or abrasion. Also, the disclosure teaches receivers through which colorants penetrate and are therefore best suited for dyes and not for pigments, especially where it is undesirable for the pigment particles to penetrate the pores in the receiver surface.
In U.S. Pat. No. 5,764,262 (E.I. Du Pont de Nemours and Co.) a method for forming a durable image is disclosed in which a pigmented ink is printed on a receiver comprised of a hydrophilic cross-linkable thermoplastic polymer. The image is heated to encapsulate the pigment and crosslink the polymer. It would be preferred to provide a receiver without the processing disadvantages of cross-linking chemistries and without the need to encapsulate the pigment.
There is therefore a need in the art for further improvement to produce high gloss and abrasion resistance in ink jet printing systems.